Slow air-lock bubbling can continue for an extended period of time in the perfectly sealed fermenter. Ascertain the correct time at which to bottle by either using your hydrometer or alternately by the visual signs. If you take two hydrometer readings 24-48 hours apart and the reading is the same for both readings, fermentation is complete and it is time to bottle/keg your beer! Don’t use the air-lock to determine when to do anything, home brewers all too often leave the brew in the fermenter too long because of slow air-lock bubbling and your brew will spoil fairly quickly if not bottled/kegged at the correct time.